Oculus (architecture)

An oculus (from Latin oculus 'eye'; pl. oculi) is a circular opening in the center of a dome or in a wall. Originating in classical architecture, it is a feature of Byzantine and Neoclassical architecture.

A horizontal oculus in the center of a dome is also called opaion (from Ancient Greek ὀπαῖον (opaîon) '(smoke) hole'; pl. opaia).